In a data communication field, a packet communication system which transmits information by breaking the information into blocks and adding additional information for identifying the data has been so far adopted. For digital visual imaging communication, it is also attempted to transmit compressed image data by packetizing.
FIGS. 1 and 2 are diagrams showing exemplified formats of transmission packets.
FIG. 1 shows an example of the transmission packet for use in transmission of data packets m, m+1, m+2, . . . by sequentially arranging them, but without synchronizing them with a prescribed sync signal. Each packet comprises a header (H) for use in identifying data in the packet, transmission data and an error correction parity (P) for use in correcting errors in the packet.
On the other hand, FIG. 2 shows an example of a transmission packet for use in the transmission of M packets synchronous with, for instance, a reference cycle of the frames, etc. of video signals. In FIG. 2, one frame is comprised of k packets of data corresponding to respective columns, and each datum of the k packets is comprised of a header H, transmission data, and an error correction parity P. Further, the header H1 of the first packet (M=1) also serves as the header for use in identifying an entire data of the k packets in the n-th frame. Further, the size of the header may vary according to its column position M.
By the way, the size of these packets and the recording unit of a recording apparatus may differ from each other. In this case, packet data are recorded by converting them into a recording format. For instance, the Japanese Patent Application Tokkai-Hei 4-86181 titled as Recording Reproducing Apparatus discloses that transmitted packets are converted into recording packets with a recording format for VTRs. The recording packet disclosed in the Application Tokkai-Hei 4-86181 is comprised of screen positional information MBA (Macro Block Address) and a sync block record start positional information MBP (Macro Block Pointer), both added into the transmission data in the unit of a sync block.
FIGS. 3 and 4 are block diagrams showing the construction of the Japanese Patent Application titled as the Recording Reproducing apparatus, while FIGS. 5(a), 5(b) and 5(c) are diagrams for explaining the recording packet of the present invention.
FIG. 3 is a block diagram showing another conventional packet conversion apparatus associated with other conventional recording packets, as shown in FIGS. 5(a) and 5(b)
Transmission packet signals are supplied to a receiving circuit 1, and then are transferred to a packetizer 3 via a buffer 2. The buffer 2 is used for adjusting the timings of data processed in later stages. The packetizer 3 converts the transmission packet signal into another packet format signal suited for a recording system, e.g., VTRs.
The recording format of a VTR is basically configured by unit of recording tracks. FIGS. 5(a), 5(b) and 5(c) show three types of recording formats each configured for one record track, wherein one track is comprised of M' packets. Each packet constitutes a sync block (sync unit).
FIG. 5(a) shows an example of the recording track wherein transmission packet signals are sequentially arranged in the transmission order by the packetizer 3. That is, in this case, header and transmission data contained in the transmission packets are arranged in the recording packet in their original order. The recording packets configured in the packetizer 3 are applied to an error correction encoder 4. The error correction encoder 4 adds an error correction parity P into each of the recording packets and provides the resulted recording packets to a combiner 5. Further, an ID generator 6 generates ID data including track number ID data, sync number ID data and other important ID data, and supplies the ID data to the combiner 5. The combiner 5 combines a sync signal SYNC at the head of each recording packet, and then arranges the ID data, information data and the error correction parity P in the recording packet at a prescribed order.
Further, the recording packet shown in FIG. 5(b) represents that the headers and the information data in the transmission packets are each divided into pieces in the recording packets, respectively. In this case, the information data contained in transmission packets are provides from the buffer 2 to the-packetizer 3, while headers are provided from the buffer 2 to a header packetizer 8. The header packetizer 8 packetizes the headers and provided the resulted packets to another combiner 7. In this case, the headers are not yet contained in the output of the combiner 5. The combiner 7 arranges the information data and the headers individually and then provides the resulted recording packets.
In the recording packet, as shown in FIG. 5(a), wherein the transmission packet data are sequentially allocated, that is, all the data containing headers and parities of the transmission packets are continuously allocated, it is not possible to suppress the propagation of errors. For instance, if any error had occurred in the data within the packet, the error position will be found by an error flag. However, unless the sync signal for the transmission packet can be surely detected, it is not possible to restore the original format of the transmission packets during it decoding operation. That is, the sync block in which an error had occurred falls in same state as the packet that lacks some data. Further, it becomes impossible to carry out a correction or an interpolation, etc. on the sync block. However when the detection of the sync signal is secured, it is possible to detect the heads of the packet from data in which no errors occur.
Further, when data and a header are each divided into pieces, as shown in FIG. 5(b), the boundaries of the data will become indefinite. Then, in the case where variable-length codes, etc. are adopted, the header position of a data portion having no errors cannot be detected and a propagation of errors becomes large as in the case shown in FIG. 5(a).
So, in the conventional packet conversion apparatus as disclosed in the above-mentioned Japanese Application with the title of Recording Reproducing Apparatus, a method has been also disclosed for suppressing the propagation of errors even when variable length coded data are input as transmission data. Further, in the present invention picture data are divided into luminance blocks and color difference blocks each having a prescribed volume, respectively. Additionally, a macro block is constructed using a plurality of sub-blocks for use as a unit of predictive coding.
In FIG. 4. transmission packet signals supplied to the receiving circuit 1 are then transferred to an MB (Macro Block) head detector 11 and a header packetizer 12 via the buffer 2. The MB head detector 11 transfers the transmission data to a data packetizer 13. The MB head detector 11 also detects the head of a macro block from the transmission data and then provides the macro block information to an MBA (Macro Block Address) generator 14. The data packetizer 13 packetizes information data and then provides the packetized data to an MBP (Macro Block Pointer) generator 15 and a combiner 16.
The MBA generator 14 generates an MBA (Macro Block Address) showing an address on the screen to which the macro block corresponds and then provides it to the combiner 16. Further, the MBP generator 15 generates an MBP (Macro Block Pointer) which is the head positional information in a sync block of the macro block and then provides it to the combiner 16. The combiner 16 combines encoded data corresponding to respective screen areas following the macro block address and the macro block pointer and then provides it to the error correction encoder 4. The error correction parity P from the error correction encoder 4 and ID data from the ID generator 6 are arranged in another combiner 17. Thus, as shown in FIG. 5(c), encoded data corresponding to respective screen areas are added with an error correction parity and arranged after the sync signal (SYNC), the ID data, the MBA (Macro Block Address) and the MBP (Macro Block Pointer) in units of one sync block. Further, the header packetizer 12 packetizes headers and sends it to still another combiner 18 for multiplexing with the output of the combiner 17. Recording track data are thus formed.
As described above, in this case, the propagation of errors is suppressed by extracting the screen positional information contained in transmission packets and recording two kinds of information, i.e., the screen positional information MBA indicating the correspondence between the data and the screen, and the positional information MBP showing data positions in recording packets.
However, the apparatus shown in FIG. 4 generates the MBA and the MBP by extracting additional information contained in transmission packets where there was such a problem that the circuit scale increases greatly.
As described above, in a conventional packet conversion apparatus, in order to suppress the propagation of errors, the positional information, MBP, and the screen positional information MBA are generated by extracting additional information contained in the transmission packets when converting transmission packets into recording packets and there is such a in problem that the circuit scale increases greatly.